Filament-wound structure



Nov. 16, 1965 w. E. PON-EMON 3,217,484

FILAMENT-WOUND STRUCTURE Filed Aug. 15, 1962 INVENTOR WARREN E. PONEMON ATTORN EY 3,217,484 I FlLAMENT-WOUND STRUCTURE Warren E. Ponemon, Syosset, N.Y., assignor to Koppers Company, Inc, a corporation of Delaware Filed Aug. 15, 1962, Ser. No. 217,099 4 Claims. (U. 57--140) This invention relates to an improved filament-wound structure and method for making the same, and in particular, to a novel strand and method for making the same for use in such a structure.

Defense requirements have highlighted the importance of such devices as missile cases, rocket motor containers and deep diving submersibles. These devices must combine maximum strength with minimum weight.

For example, in order to contribute to rapid acceleration, a propellant casing must be light in weight. At such times, it is subjected to extreme and sudden stresses caused by acceleration, twisting, etc. Because of this the casing requires both maximum strength and minimum weight. Although much work has been done in the field of forming hollow elements by filament winding, the application has not been made in a manner to take full advantage of the inherent characteristics of the filaments themselves.

The basic factor limiting the strength/ weight ratio has been the strand employed to make the structure.

The product and process of this invention enable the demand to be met and eliminate the drawbacks of the prior art. Filament-wound devices are formed principally of filament material with a minor proportion of synthetic resin as a binder. Since the binding material is normally weaker than the filament, it is desirable to use a minimum amount of resin.

Briefly stated, one aspect of the invention relates to the provision of a multifilament winding strand characterized by a more compact and higher filament count per unit area than heretofore employed, and in another aspect relates to structures employing such high density filaments. The multifilament strand is composed of filaments of at least two different diameters. The smaller diameter is chosen to fit in the voids formed between adjacent ones of larger diameter.

Since typical glass fibers employed for filament winding have a diameter of but 0.00036, it is not readily appreciated that a significant increase in strength can be obtained by filling the voids.

By filling most of the void areas with additional fibers instead of binding material or other strengthening material or materials, this invention achieves a strand of enhanced strength characteristics.

Accordingly, it is the object of this invention to provide a strand composed of fibers in such a way as to yield improved properties.

In particular, it is the object of this invention to increase the strength of the strand.

These and other objects and advantages of this invention will, in part, be pointed out with particularity and will, in part, become obvious from the following preferred embodiment of this invention, taken in conjunction with the accompanying drawing which forms an integral part thereof.

In the various figures of the drawing, like reference characters designate like parts.

In the drawing:

FIG. 1 is an enlarged transverse cross-section of the filament bundle of this invention.

FIG. 2 is a greatly enlarged transverse cross-section of an alternative embodiment of a filament bundle.

FIG. 3 is a greatly enlarged transverse cross-section of still another alternative embodiment of a filament bundle.

. United States Patent 3,217,484 Patented Nov. re, 1965 FIG. 4 is a greatly enlarged transverse cross-section of a portion of the resin bonded filament-wound structure.

Referring now to FIG. 1, there is shown a plurality of fibers 10 of a large diameter of say 0.0003 6. Whereas in the prior art structure, the voids between fibers were filled with resin, part of the binding material which formerly had occupied the spaces between fibers 110 has been replaced with fibers 12 of a smaller diameter. The smaller fibers I2 occupy the voids created by the tangential contact within groups of three larger diameter filaments 10. Surprisingly, for a bundle of but 234 large filaments 10 there is room for as many as 484 smaller fibers 12. Larger sized bundles can accommodate an even larger number of filaments of small fibers.

The limiting or maximum diameter of these smaller fibers may be calculated from geometrical and trigonometric considerations.

Assuming the diameters of the original fibers 10 are 0.00036", then the diameters of the small filaments are 0.000060", or about 15.5% of the diameters of the large filaments.

The strength of the fiber bundle may be increased still further, as shown in FIG. 2. On the periphery in the void created by tangential contact of two large diameter fibers 10, additional fibers 12a may be inserted. The diameters of these fibers may be the same as those of the fibers 12 inserted in the interstices formed by three of the large diameter fibers 10. If, for example, the bundling or stranding pattern of FIG. 1 is employed there will be 234 large diameter filaments 10. There may be interposed among them, in the manner hereinbefore described, 484 filaments 12 having a diameter of 0.000060 and an addition 60 fibers 12a (around the periphery) also having a diameter of 0.000060".

Remembering that the area of a circle is proportional to the square of its diameter, the percentage increase in area provided by the 544 additional fibers 12 and 12a may now be calculated as by the following examples which illustrate the quantitative rise in strength:

Example A (FIG. 1) 484 (6) 234 (36) Example B (FIG. 2) 544 (6) 234 (36) It should be noted that this figure may be increased by inserting additional even smaller fibers 14 in the interstices formed by two of the larger fibers l0 and one of the smaller fibers 12, as seen in FIG. 3.

Since the diameter of these smallest fibers 14 is approximately 0.000025 the structure will accommodate 3 times 484, or 1452 of theses mallest fibers. The percentage increase in strength due to the use of these even smaller fibers is as follows: Example C (FIG. 3)

Thus, the embodiment of FIG. 3 yields a total increase in strength of 6.4% +2.2%:8.6%.

It is preferred to employ, as smaller fibers 12, about one to two times the number of the larger fibers 10. The smaller fibers 12 should have a diameter about one-sixth the diameter of the larger fibers. It is to be appreciated that an even larger number of finer filaments may be used to fill the voids between the primary filaments. If the fiber employed permits the drawing of an extremely fine diameter, then the embodiment of FIG. 3 may be used.

X 5.7% increase X 100 6.4 increase 3 In this case, the extremely small fibers should be about one thirty-sixth of the diameter of the largest size and be present in about the numerical ratio of about one of the largest to two of the smallest fibers.

The composite strand of this invention may be produced in situ by simultaneously extruding, or drawing a bundle of fibers of the proper size distribution.

On the other hand, the bundle may be assembled from separately produced fibers of different diameter.

It is to be appreciated that the number of interstices increase rapidly with the size of the bundle. Thus, starting with a single central filament and surrounding it with like filaments in concentric layers, it will be found that voids increase in each layer by 211-6 where n is the number of filaments in a ring. In the example, a 10-ring bundle was studied.

In FIG. 4, there is shown in an enlarged cross-section a portion of a resin bonded filament winding. In winding, a resin-impregnated strand may be employed, or the winding may be post-impregnated preferably by vacuum impregnation techniques.

Although numerous different types of fibrous materials may be used, nevertheless glass fibers are currently preferred. Glass fibers may be economically produced in substantially continuous lengths in the microscopic diameters mentioned. The composite bundle of different sized fibers may be simultaneously drawn by standard filament drawing techniques.

The choice of a binding material 18 offers wide latitude. It is presently preferred to use the so-called epoxide resins. Epoxide compounds are those compounds having an ether oxygen atom joined to two vicinal carbon atoms. The term epoxide resin denotes the resinous reaction product of certain of these epoxide compounds and compounds having available hydrogen atoms linked to carbon atoms, as for example, polyhydric phenols and polyhydric alcohols. A particularly useful epoxide resin is the reaction product of an epihalohydrin and a polyhydric phenol, as exemplified by bisphenol-epichlorhydrin. Other equivalent epoxide resins are well known to those skilled in the plastics art.

In this specification, including the appended claims, the following terms have the following corresponding meanmgs:

The cross-sectional area of a resin bonded wound member occupied by resin is considered to be a void.

An interstice is the small space between a group of adjacent filaments.

An interstitial fiber is a fiber placed in the interstice between the adjacent filaments.

Periphery refers to the space or area surrounding the outer layer of a bundle of filaments.

Thus it is seen that void includes interstice and periphery.

A fiber is a slender threadlike element of a substance such as spun glass. Fiber and filament are herein synonymous.

A strand is composed of a bundle of filaments, threads, fibers, etc. Strands are frequently twisted together to form a length of string, rope, etc. thus composed of several strands of fiber.

A string or rope is Since the fibers may be drawn (pulled through orifices) as well as extruded (forced through orifices), the term extruded, as used in the appended claims, includes drawn.

In summary, the trength of a filament-wound structure increases in direct proportion to the fiber area, and will exhibit structural properties the magnitude of which has been hitherto unattainable.

It is to be understood that various changes, omissions and additions may be made to the preferred embodiment of the invention herein described, without departing from the spirit of the invention.

Having thus described the best embodiment of the invention presently contemplated, what is claimed is:

1. An untwisted strand of uniform tensile strength and weight throughout the length thereof, said strand being suitable for forming a resin impregnated filament wound structure comprising a plurality of continuous longitudinally disposed first synthetic fibers and a plurality of continuous, longitudinally disposed second synthetic fibers of smaller diameter and of substantially larger number than said first fibers, said first fibers being of sufficient number and size whereby they are in tangential contact with each other to define a plurality of first, longitudinal voids of substantially equal size therebetween, a plurality of said second fibers arranged about the circumference of almost all of said first fibers whereby said second fibers are disposed in the first voids created by the tangential contact of at least two of said first fibers, said first and second fibers further defining, in combination, a plurality of second equally sized smaller voids between two of said first fibers and one of said second fibers.

2 The strand of claim 1 including a plurality of continuous, longitudinally disposed third synthetic fibers of substantially smaller diameter than said first and second fibers, said third fibers being disposed in the second, smaller sized voids defined by the contact of two of said first fibers and one of said second fibers, a plurality of said third fibers arranged about the circumference of almost all of said second fibers and in tangential contact with said first and second fibers.

3. The strand of claim 2 wherein the total number of said third fibers is substantially greater than that of said first fibers.

4. The strand of claim 1 wherein the fibers are glass and the resin is an epoxy.

References Cited by the Examiner UNITED STATES PATENTS 2,461,094 2/1949 Taylor 57-14O 2,562,340 7/1951 Stanton 57-145 2,856,750 10/1958 Lewis 57153 2,917,891 12/1959 Murdock 57153 X 3,018,606 1/1962 Dietz 57148 3,029,589 4/1962 Caroselli et al 57153 MERVIN STEIN, Primary Examiner.

RUSSELL C. MADER, Examiner. 

1. AN UNTWISTED STRAND OF UNIFORM TENSILE STRENGTH AND WEIGHT THROUGHOUT THE LENGTH THEREOF, SAID STRAND BEING SUITABLE FOR FORMING A RESIN IMPREGNATED FILAMENT WOUND STRUCTURE COMPRISING A PLURALITY OF CONTINUOUS LONGITUDINALLY DISPOSED FIRST SYNTHETIC FIBERS AND A PLURALITY OF CONTINUOUS, LONGITUDINALLY DISPOSED SECOND SYNTHETIC FIBERS OF SMALLER DIAMETER AND OF SUBSTANTIALLY LARGER NUMBER THAN SAID FIRST FIBERS, SAID FIRST FIBERS BEING OF SUFFICIENT NUMBER AND SIZE WHEREBY THEY ARE IN A TANGENTIAL CONTACT WITH EACH OTHER TO DEFINE A PLURALITY OF FIRST, LONGITUDINAL VOIDS OF SUBSTANTIALLY EQUAL SIZE THEREBETWEEN, A PLURALITY OF SAID SECOND FIBERS ARRANGED ABOUT THE CIRCUMFERENCE OF ALMOST ALL OF SAID FIRST FIBERS WHEREBY SAID SECOND FIBERS ARE DISPOSED IN THE FIRST VOIDS CREATED BH THE TANGENTIAL CONTACT OF AT LEAST TWO OF SAID FIRST FIBERS, SAID FIRST AND SECOND FIBERS FURTHER DEFINING, IN COMBINATION, A PLURALITY OF SECOND EQUALLY SIZED SMALLER VOIDS BETWEEN TWO OF SAID FIRST FIBERS AND ONE OF SAID SECOND FIBERS. 